In surgical procedures involving the spine, it is common to secure a pair of spinal rods to a series of vertebrae so that the rods are aligned essentially parallel to the spinal column. The spinal rods may serve to immobilize vertebrae, preventing unwanted flexion, extension, and rotation of vertebrae with respect to each other. It is often further desirable, or even necessary, to provide a connecting device to extend transversely between spinal rods, thereby securing the spinal rods relative to each other.
Spinal rods are typically anchored to the vertebrae via bone screws that extend through the pedicle into the vertebral bodies or by hooks that engage about the vertebrae. The spinal rods are connected to the screws or anchor members by coupling members designed to receive and secure a rod. For instance, the coupling member may be yoke-shaped with a cap to close and lock the open end of the yoke. Such coupling members may be integral with the anchor member, or may be provided as a separate component in order to allow for polyaxial movement of the anchor member.
Surgical procedures involving the spine benefit from minimal invasiveness of the surgery and from having a low-profile for any fixtures secured in the body. While incisions are required during such surgical procedures in order to gain access to the site where the implant is secured, such incisions can cause damage, injury, and trauma to the patient's body. To avoid causing unnecessary damage, it is preferable to make the incisions as small and as few as possible. The ease of recovery and mobility of a patient with spinal fixtures is greatly influenced by the invasiveness of the procedure and by the size of any spinal fixtures. To this end, minimally invasive surgery systems (MISS) have been developed to minimize trauma to the patient, such as the system described in WO 06091863, the subject matter of which is hereby incorporated by reference as if fully set forth herein, wherein in certain embodiments a docking sleeve is inserted into a small incision to provide a portal through which the implantation procedure may be performed. Such a docking sleeve may also have docking fasteners in order to fix the docking sleeve to bone during the surgical procedure.
When utilizing crosslinking or connecting devices to secure pedicle screws, a number of obstacles are commonly encountered. Spinal rods are mounted by a surgeon in a custom-fit manner, including some bending of the rod, so that the rod extends properly along the spine for holding the vertebral portions in proper relation. Accordingly, there is often not a predetermined distance between two spinal rods, and the rods may converge or diverge from each other. In addition, one spinal rod may have a portion directed at an angle or curve different from that of the other rod. Therefore, the central axes of the two spinal rods may be skewed, pivoted, or rotated relative to each other.
One attempt at overcoming these obstacles and to facilitate linking of non-parallel portions of spinal rods is a crosslinking system that includes two opposed ends comprising clamping devices for securing the spinal rods, with the clamping devices linked to each other by a central cross rod or rods, typically allowing three degrees of movement. That is, the central cross rod is attached to the connecting devices in a manner that provides articulation points that allow (i) adjustment of the distance between the connector ends by axial movement of the cross rod; (ii) pivotal adjustment of at least one connecting device about one end of the cross rod; and (iii) rotation of the connecting devices relative to each other about the axis of the cross rod.
However, providing multiple points of articulation presents further problems. For instance, the components of the cross connector must be configured in such a way that they do not interfere with each other when arranged in various configurations. Furthermore, each articulation point must be capable of locking in order to secure the spinal rods in a desired configuration, requiring multiple locking mechanisms that must be loosened and tightened in order to adjust and secure the cross connector. Additionally, cross connectors with multiple points of articulation and multiple locking mechanisms are often difficult to implement in MISS applications, since the surgeon must gain access to each of the locking mechanisms, which in many transverse connector systems are located on the cross rod portion traversing the gap between the two spinal rods. Thus, the surgeon must make additional incisions at points between the implanted spinal rods in order to adjust and secure the cross connector.
Furthermore, it is common for the connecting ends of a transverse connector to have a hook portion extending around a spinal rod and pointing back towards the center of the transverse connector for securing to a spinal rod. In such an arrangement, installation or implantation of the device requires clearance laterally of the spinal rods so that the hook portion can be placed outside of the spinal rod and then drawn inward for securing the rod. Often, the patient's soft tissue must be cleared for this purpose, a result which may exacerbate pain, discomfort, and healing time.
In addition, many connecting members utilize set screws. For instance, set screws may be utilized for securing the hook portion to the spinal rod, and a set screw may be utilized for securing one connector end relative to the other. A set screw generally only provides a line or point contact with the surface against which it is driven. When a set screw drives against a spinal rod or other fixture, damage and distortion may occur at the interface. This can lead to uneven securement by the set screw, localized weakening of the fixture, loosening of the screw, or debris ground from either the screw or the fixture. Additionally, the screws require a threaded path long enough to provide a secure hold for the screw, which adds to the material cost, to the size of the fixture, and to the invasiveness of the procedure. Use of set screws also often requires use of a torque driver to insure that the screws are not over-tightened.
Moreover, the use of a set screw in the central fastening area presents a danger to the patient. The connecting member spans the dura portion of the spine. Put simply, portions of the spine other than bone, such as the discs or even the spinal cord itself, may be exposed. Use of a driver to tighten set screws on the transverse connector exposes the non-bone spinal portions to damage caused by the driver slipping from the set screw and punching into the discs or spinal cord in, for instance, in awl-like fashion.
Accordingly, there has been a need for an improved transverse connector for securing spinal rods relative to each other.